Method Of And A Composition For Controlling Gas Hydrate Blockage Through The Addition Of A Synergistically Acting Blend With N-Alkanoyl-Polyhydroxyalkylamines

ABSTRACT

The present disclosure relates to a gas hydrate inhibitor composition comprisingA) a compound according to formula (1)whereinR1 is an alkyl group having from 1 to 5 carbon atoms;R2 is hydrogen or an alkyl group having from 1 to 5 carbon atoms;R3 is present or not as hydrogen and organic moieties having from 1 to 20 carbon atoms;R4 is selected from —(CH2)t-, —[(CH2-CHR6)t]-, —(CH2-CHR6O)u-(CH2)t- and combinations thereof;R5 is an alkyl or alkenyl group having 4 to 22 carbon atoms;R6 is hydrogen or an alkyl group having from 1 to 4 carbon atoms;R7 is hydrogen or an alkyl group having from 1 to 4 carbon atoms;R8 is present or not as hydrogen or organic moieties having from 1 to 20 carbon atoms;t is 2, 3 or 4;u is an integer between 0 and 100;n is 0 or 1m is 0 or 2o is 0 or 2p is 0 or 1X− is an anion,andand a a synergistic surfactant which is selected from the group consisting of N-acylated polyhydroxyalkylamines and a method of using the gas hydrate inhibitor composition.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to co-pending U.S. Provisional PatentApplication No. 62/946,679, filed Dec. 11, 2019, the entirety of whichis hereby incorporated herein by reference.

This invention relates to the prevention of gas hydrate blockage in oiland natural gas pipelines containing low-boiling point hydrocarbons andwater. More specifically, the invention relates to a method ofcontrolling gas hydrate blockage through the addition of asynergistically acting blend of chemical compositions.

When hydrocarbon gas molecules dissolve in water, the hydrogen-bondednetwork of water molecules encapsulates the gas molecules to form acage-like structure or hydrate. Higher pressures and lower temperaturesfoster the formation of these structures. These hydrates grow byencapsulating more and more gaseous molecules to form a crystallinemass. The crystalline mass agglomerates to form a larger mass that canresult in a plugged transmission line. The hydrocarbon gases that formthe majority of the hydrates include methane, ethane, propane, n-butane,iso-butane, n-pentane, iso-pentane, and combinations of these gases.

Thermodynamic hydrate inhibitors, such as methanol or one of theglycols, have traditionally been used to prevent these hydrateformations. These thermodynamic inhibitors are effective at 5-50% (orhigher) based on the amount of water. As oil companies are exploring newproduction in deep waters, the total gas/oil/water productions are alsoincreasing. The use of these thermodynamic inhibitors is not viable inthese applications due to logistical constraints of supplying andpumping such vast quantities of fluids to often remote locations.

Kinetic hydrate inhibitors have been identified to prevent these hydrateformations so that the fluids can be pumped out before a catastrophichydrate formation occurs. The kinetic inhibitors prevent or delayhydrate crystal nucleation and disrupt crystal growth. These kinetichydrate inhibitors contain moieties similar to gas molecules previouslymentioned. It is suspected that these kinetic inhibitors prevent hydratecrystal growth by becoming incorporated into the growing hydratecrystals, thereby disrupting further hydrate crystal growth. The growinghydrate crystals complete a cage by combining with the partialhydrate-like cages around the kinetic hydrate inhibitor moietiescontaining gas-like groups. These inhibitors are effective with orwithout the presence of a liquid hydrocarbon phase, but they aretypically less effective in preventing the hydrate formation as theproduction pressure increases. Examples of kinetic hydrate inhibitorsinclude poly(N-methylacrylamide), poly(N,N-dimethylacrylamide),poly(N-ethylacrylamide), poly(N,N-diethylacrylamide),poly(N-methyl-N-vinylacetamide), poly(2-ethyloxazoline),poly(N-vinylpyrrolidone), and poly(N-vinylcaprolactam).

Unlike the kinetic hydrate inhibitors, anti-agglomerates are effectiveonly in the presence of an oil phase. Anti-agglomerates do not inhibitthe formation of gas hydrates to the same level as kinetic inhibitors,rather their primary activity is in preventing the agglomeration ofhydrate crystals. The oil phase provides a transport medium for thehydrates which are referred to as hydrate slurries so that the overallviscosity of the medium is kept low and can be transported along thepipeline. As such, the hydrate crystals formed in the water-droplets areprevented from agglomerating into a larger crystalline mass.

Examples of several chemicals acting as anti-agglomerates have beenreported in U.S. Pat. Nos. 5,460,728; 5,648,575; 5,879,561; and6,596,911. These patents teach the use of quaternary ammonium saltshaving at least three alkyl groups with four or five carbon atoms and along chain hydrocarbon group containing 8-20 atoms. Exemplarycompositions include tributylhexadecylphosphonium bromide andtributylhexadecylammonium bromide.

U.S. Pat. No. 5,460,728 teaches the use of alkylated ammonium,phosphonium or sulfonium compounds having three or four alkyl groups intheir molecule, at least three of which are independently chosen fromthe group of normal or branched alkyls having four to six carbon atoms.

U.S. Pat. No. 5,648,575 teaches very similar compositions having threeor four organic groups in their molecule, at least three of which haveat least four carbon atoms, i.e., two normal or branched alkyl groupshaving at least four carbon atoms and with a further organic moietycontaining a chain of at least four carbon atoms.

U.S. Pat. No. 5,879,561 teaches the use of alkylated ammonium orphosphonium compounds having four alkyl groups, two of which areindependently normal or branched alkyls having four or five carbon atomsand two more of which independently represent organic moieties having atleast eight carbon atoms.

U.S. Pat. No. 6,369,004 B1 teaches the kinetic inhibition of gas hydrateformation using polymers based on reacting maleic anhydride with one ormore amines. These polymers can also be used together with various othersubstances, called synergists, including tetrabutylammonium salts,tetrapentylammonium salts, tributylamine oxide, tripentylamine oxide,zwitterionic compounds having at least one butyl or pentyl group on thequaternary ammonium nitrogen atom, such as as Bu₃N⁺—CH₂—COO⁻. However,kinetic inhibitors are not effective as the pipeline pressure increases.

U.S. Pat. No. 6,015,929 teaches the use of specific zwitterioniccompounds such as R(CH₃)₂N⁺—(CH₂)₄—SO₃ ⁻ as anti-agglomerates. Thesynthesis of this product involves the use of butyl sulfone.

U.S. Pat. No. 7,381,689 teaches a method and an amide composition usedtherein for inhibiting, retarding, mitigating, reducing, controllingand/or delaying formation of hydrocarbon hydrates or agglomerates ofhydrates. The method may be applied to prevent or reduce or mitigateplugging of conduits, pipes, transfer lines, valves, and other places orequipment where hydrocarbon hydrate solids may form under theconditions. At least one amide compound is added into the processstream, where the compound may be mixed with another compound selectedfrom amino alcohols, esters, quaternary ammonium, phosphonium orsulfonium salts, betaines, amine oxides, other amides, simple aminesalts, and combinations thereof.

However, there remains a need for hydrate inhibitor compounds thateffectively prevent agglomeration of hydrates in oil and gastransportation and handling processes. It would be desirable to identifyhydrate inhibitor compounds that are effective at lower dosages, higherpressures and/or lower temperatures such as those encountered in deepwater production.

Surprisingly, it has been found that a gas hydrate inhibitor thatcomprises an amidoamine of a fatty acid, which optionally is in the formof a cationic ammonium compound, will be enhanced in its performance asa gas hydrate inhibitor when used together in a mixture with asynergistic surfactant which comprises a nonionic surfactant which isselected from the group consisting of N-acylated polyhydroxyalkylamines.

In a first embodiment, the instant invention provides a gas hydrateinhibitor composition, comprising

A) from 5 to 95 weight-% of a compound according to formula (1)

wherein

-   R1 is an alkyl group having from 1 to 5 carbon atoms;-   R2 is hydrogen or an alkyl group having from 1 to 5 carbon atoms;-   R3 is present or not as hydrogen and organic moieties having from 1    to 20 carbon atoms;-   R4 is selected from —(CH₂)_(t)—, —[CH₂—CHR⁶)_(t)]—,    —(CH₂—CHR⁶O)_(u)—(CH₂)_(t)— and combinations thereof;-   R5 is an alkyl or alkenyl group having 4 to 22 carbon atoms;-   R6 is hydrogen or an alkyl group having from 1 to 4 carbon atoms;-   R7 is hydrogen or an alkyl group having from 1 to 4 carbon atoms;-   R8 is present or not as hydrogen or organic moieties having from 1    to 20 carbon atoms;-   t is 2, 3 or 4;-   u is an integer between 0 and 100;-   n is 0 or 1-   m is 0 or 2-   o is 0 or 2,-   p is 0 or 1-   X⁻ is an anion,    and    B) from 5 to 95 weight-% of a compound that is a synergistic    surfactant which is selected from the group consisting of N-acylated    polyhydroxyalkylamines according to formula (19)

wherein

-   Z is the polyhydroxyalkyl radical of a monosaccharide or    oligosaccharide;-   R¹¹ is an alkyl or alkenyl group having 8 to 18 carbon atoms; and-   R¹² is an alkyl group having from 1 to 5 carbon atoms.

The synergistic surfactant is a surfactant that enhances the effect ofthe gas hydrate inhibitor. Whether or not there is a synergy betweencomponents A) and B) is determined by the reduced dose rate to preventgas hydrate agglomeration over the dose rate required of each of theindividual components. The reduction of dosage rate is at least 10-40wt. %, preferably 20-40 wt. % and most preferably 25-40 wt. %.

In a preferred embodiment, the instant invention provides a gas hydrateinhibitor composition, wherein A) is a compound according to formula(1a)

wherein

-   R1 is an alkyl group having from 1 to 5 carbon atoms;-   R2 is hydrogen or an alkyl group having from 1 to 5 carbon atoms;-   R3 is present or not as hydrogen and organic moieties having from 1    to 20 carbon atoms;-   R4 is selected from —(CH₂)_(t)—, —[CH₂—CHR⁶)_(t)]—,    —(CH₂—CHR⁶O)_(u)—(CH₂)_(t)— and combinations thereof;-   R5 is an alkyl or alkenyl group having 4 to 22 carbon atoms;-   R6 is hydrogen or an alkyl group having from 1 to 4 carbon atoms;-   R7 is hydrogen or an alkyl group having from 1 to 4 carbon atoms;-   R8 is present or not as hydrogen or organic moieties having from 1    to 20 carbon atoms;-   t is 2, 3 or 4;-   u is an integer between 0 and 100;-   n is 0 or 1-   m is 0 or 2-   o is 0 or 2,-   p is 0 or 1,-   q is an integer between 0 and 2-   X⁻ is an anion,    wherein q is 0 when R3 and R8 are absent; q is 1 when one of R3 and    R8 is present and the other is absent; and q is 2 when R3 and R8 are    both present.

In a preferred embodiment, the polyhydroxyalkyl radical Z is derivedfrom monosaccharides such as erythrose, threose, ribose, arabinose,xylose, lyxose, allose, altrose, glucose, mannose, gulose, idose,galactose, talose or fructose, or derivatives thereof such as glucuronicacid or deoxyribose or oligosaccharides and disaccharides such assaccharose, lactose, trehalose, maltose, cellobiose or gentiobiose, andalso from trisaccharides such as raffinose. Also suitable are allcommercial starch degradation products such as glucose syrup ordextrins, eg, maltodextrins. In a preferred embodiment, Z is apolyhydroxyalkyl radical derived from aldohexoses and having the formula—CH₂—(CHOH)₄—CH₂—OH. Particularly preferred is the radical of glucoseand especially of naturally occurring D(+)-glucose. Derived frommonosaccharide or oligosaccharide means that the carbonyl group of thesaccharide has been transformed into an amino group, for example byreductive amination with an amine of formula NH—R¹².

In a preferred embodiment, R¹¹ is an alkyl or alkenyl group having from8 to 16 and more preferred from 10 to 14 carbon atoms, as for examplefrom 8 to 14, or from 10 to 18, or from 10 to 16 carbon atoms. The alkylor alkenyl group may be linear or branched. Preferably it is linear.Unsaturated alkenyl groups R¹¹ contain one or two double bonds. Examplesfor preferred alkyl and alkenyl groups are octyl, 2-ethyl hexyl,iso-nonyl, decyl, iso-undecyl, dodecyl, iso-tridecyl, tetradecyl,pentadecyl, hexadecyl, octadecyl, oleyl, and any mixtures thereof. In apreferred embodiment, R¹¹ comprises a mixture of different alkyl and/orgroups within the given chain lengths.

In a preferred embodiment, R¹¹ together with the carbonyl group to whichit is attached, is derived from a fatty acid. Preferred fatty acids areselected from the group consisting of capric acid, lauric acid, stearicacid, myristic acid, myristoleic acid, palmitic acid, palmitoleic acid,stearic acid, sapienic acid, elaidic acid, vaccenic acid, linoleic acid,oleic acids (cis- and trans-), and any combination thereof. In apreferred embodiment, the fatty acid is obtained from a plant source oran animal source selected from corn oil, canola oil, coconut oil,safflower oil, sesame oil, palm oil, cottonseed oil, soybean oil, oliveoil, sunflower oil, hemp oil, wheat germ oil, palm kernel oil, or tallowoil, vegetable oil, and combinations thereof.

The radical R¹² denotes hydrogen or C₁-C₄ alkyl such as methyl, ethyl,n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, orn-pentyl. Of these, methyl is especially preferred.

The nonionic surfactants (B) and their methods of preparation are wellknown to the ones skilled in the art. For example, the N-acylatedpolyhydroxyalkylamines according to formula (19) can be manufactured byreductive amination of mono- and oligosaccharides with an amine offormula NH—R¹² and subsequent amidation of the amine with a carboxylicacid of formula R¹²—COOH or its reactive equivalent, as for example itsester with a C₁-C₄ alcohol, its acid chloride, or its anhydride.

A surfactant as defined herein is a compound that will decrease thesurface tension when added to the aqueous compositions as describedherein. In a comparison of the aqueous composition with and withoutsurfactant, the aqueous composition with surfactant needs to have alower surface tension.

Additional surfactants for use in the present invention typicallycontain hydrophobic groups such as alkenyl, cycloalkenyl, alkyl,cycloalkyl, aryl, alkyl/aryl or more complex aryl (as in petroleumsulfonates) moieties being from C₈ to C₂₂, preferably C₁₀ to C₂₀,typically C₁₂ to C₁₈, and a hydrophilic moiety which preferably is apolyethoxy group with 5 to 20 ethoxy units. Other hydrophobic groupsincluded in the invention are polysiloxane groups and polyoxypropylenegroups.

The additional surfactant may for example comprise or consist of an atleast sparingly water-soluble salt of sulfonic or mono-esterifiedsulfuric acids, for example an alkylbenzene sulfonate, alkyl sulfate,alkyl ether sulfate, olefin sulfonate, alkane sulfonate, alkylphenolsulfate, alkylphenol ether sulfate, alkylethanolamide sulfate,alkylethanolamidether sulfate, or alpha sulfo fatty acid or its estereach having at least one alkyl or alkenyl group with from C₈ to C₂₂,more usually C₁₀ to C₂₀, aliphatic atoms.

The expression “ether” here-in-before refers to compounds containing oneor more glyceryl groups and/or an oxyalkylene or polyoxyalkylene groupespecially a group containing from 1 to 150 oxyethylene and/oroxypropylene groups. One or more oxybutylene groups may additionally oralternatively be present. For example, the sulfonated or sulfatedsurfactant may be sodium dodecyl benzene sulfonate, potassium hexadecylbenzene sulfonate, sodium dodecyl, dimethyl benzene sulfonate, sodiumlauryl sulfate, sodium tallow sulfate, potassium oleyl sulfate, ammoniumlauryl sulfate, sodium tallow sulfate, potassium oleyl sulfate, ammoniumlauryl monoethoxy sulfate, or monoethanolamine cetyl 10 mole ethoxylatesulfate.

Further anionic surfactants which may be added to the current inventioninclude alkyl sulfosuccinates, such as sodium dihexylsulfosuccinate,alkyl ether sulfosuccinates, alkyl sulfosuccinamates, alkyl ethersulfosuccinamates, acylsarcosinates, acyl taurides, isethionates, soapssuch as stearates, palmitates, resinates, oleates, linoleates and alkylether carboxylates.

Anionic phosphate esters and alkyl phosphonates, alkylamino and iminomethylene phosphonates may additionally be used. In each case thefurther anionic surfactant typically contains at least one alkyl oralkenyl chain having from C₈ to C₂₂, preferably C₁₀ to C₂₀. In the caseof ethers, there is one or more glyceryl group, and/or from 1 to 150oxyethylene and/or oxypropylene and/or oxybutylene groups. Preferredanionic surfactants are sodium salts. Other salts of commercial interestinclude those of potassium, lithium, calcium, magnesium, ammonium,monoethanolamine, diethanolamine, triethanolamine, alkyl aminescontaining up to seven aliphatic carbon atoms, and alkyl and/or hydroxylalkyl phosphonium.

The surfactant component of the present invention may further contain orconsist of non-ionic surfactants. The non-ionic surfactant may be forexample C₈ to C₂₂ alkanolamides of a mono or di-lower alkanolamine, suchas coconut monoethanolamide. Other non-ionic surfactants which mayoptionally be present, include tertiary acetylenic glycols,polyethoxylated alcohols, polyethoxylated mercaptans, glucamines andtheir alkoxylates, glucamides and their alkoxylates,alkylpolyglucacides, polyethoxylated carboxylic acids, polyethoxylatedamines, polyethoxylated alkylolamides, polyethoxylated alkylphenols,polyethoxylated glyceryl esters, polyethoxylated sorbitan esters,polyethoxylated phosphate esters, and the propoxylate or ethoxylated andpropoxylated analogues of all the aforesaid ethoxylated non-ionics, allhaving a C₈ to C₂₂ alkyl or alkenyl group and up to 20 ethyleneoxyand/or propyleneoxy groups. Also included arepolyoxypropylene/polyethylene oxide block copolymers,polyoxybutylene/polyoxyethylene copolymers andpolyoxybuylene/polyoxypropylene copolymers. The polyethoxy,polyoxypropylene and polyoxybutylene compounds may be end capped with,for example benzyl groups to reduce the foaming tendency.

Compositions of the present invention may further contain an amphotericsurfactant. The amphoteric surfactant may for example be a betaine, forexample a betaine of the formula (R¹³)₃N⁺CH₂COO⁻, wherein each R¹³ maybe the same or different and is an alkyl, cycloalkyl, alkenyl or alkarylgroup and preferably at least one, and more preferably not more than oneR¹³ has an average of from C₈ to C₂₀, for example C₁₀ to C₁₈ of analiphatic nature and each other R¹³ has an average of from C₁ to C₄.

Additional amphoteric surfactants for use according to the currentinvention include quaternary imidazolines, alkyl amine ether sulfates,sulfobetaines and other quaternary amine or quaternised imidazolinesulfonic acids and their salts, and zwitterionic surfactants, forexample N-alkyl taurines, carboxylates amidoamines such asR¹⁴CONH(CH₂)₂N″(CH₂CH₂CH₃)₂CH₂CO⁻ ₂ and amido acids having, in eachcase, hydrocarbon groups capable of conferring surfactant properties(R¹⁴ is either alkyl, cycloalkyl alkenyl or alkaryl groups having fromC₈ to C₂₀ of an aliphatic nature). Typical examples include 2-tallowalkyl, 1-tallow amido alkyl, 1-carboxymethyl imidazoline and 2-coconutalkyl N-carboxymethyl 2 (hydroxyalkyl) imidazoline. Generally speaking,any water soluble amphoteric or zwitterionic surfactant compound whichcomprises a hydrophobic portion including C₈ to C₂₀ alkyl or alkenylgroup and a hydrophilic portion containing an amine or quaternaryammonium group and a carboxylate, sulfate or sulfonic acid group may beused in the present invention.

Compositions of the current invention may further contain otheramphoteric surfactant such as an amine oxide, for example an amine oxidecontaining one or two (preferably one) C₈ to C₂₂ alkyl group, theremaining substituent or substituents being preferably lower alkylgroups, for example C₁ to C₄ alkyl groups or benzyl groups. Particularlypreferred for use according to the current invention are surfactantswhich are effective as wetting agents, typically such surfactants areeffective at lowering the surface tension between water and ahydrophobic solid surface. Surfactants are preferred which do notstabilize foams to a substantial extent.

Compositions of the present invention may also include additionalcationic surfactants. The additional cationic surfactant may for examplebe a quaternary ammonium compound of the formula (6):

wherein

-   R¹⁸ is a C₅ to C₂₁ aliphatic hydrocarbon group,-   X is an anionic counter ion, and-   R¹⁵, R¹⁶, R¹⁷ are most typically selected from the group consisting    of hydrogen, methyl, ethyl, allyl, propyl, butyl, phenyl or benzyl    residues.

Further alkylammonium surfactants for use according to the inventionhave one or at most two long aliphatic chains per molecule (for examplechains having an average of C₈ to C₂₀ each, usually C₁₂ to C₁₈ and twoor three short chain alkyl groups having C₁ to C₄ each, for examplemethyl or ethyl groups, preferably methyl groups. Typical examplesinclude dodecyl trimethyl ammonium salts. Benzalkonium salts having oneC₈ to C₂₀ alkyl group, two C₁ to C₄ alkyl groups and a benzyl group arealso useful. Another useful class of cationic surfactant according tothe present invention comprises N-alkyl pyridinium salts wherein thealkyl group has an average of from C₈ to C₂₂, preferably C₁₀ to C₂₀.Other similarly alkylated heterocyclic salts, such as N-alkylisoquinolinium salts, may also be used. Alkylaryl dialkylammonium saltsin which the alkylaryl group is an alkyl benzene group having an averageof from C₈ to C₂₂, preferably C₁₀ to C₂₀ and the other two alkyl groupsusually have from C₁ to C₄, for example methyl groups are useful. Otherclasses of cationic surfactant which are of use in the present inventioninclude so called alkyl imidazoline or quaternized imidazoline saltshaving at least one alkyl group in the molecule with an average of fromC₈ to C₂₂ preferably C₁₀ to C₂₀. Typical examples include alkyl methylhydroxyethyl imidazolinium salts, alkyl benzyl hydroxyethylimidazolinium salts, and 2 alkyl-1-alkylamidoethyl imidazoline salts.Another class of cationic surfactant for use according to the currentinvention comprises the amido amines such as those formed by reacting afatty acid having C₂ to C₂₂ or an ester, glyceride or similar amideforming derivative thereof, with a di or poly amine, such as, forexample, ethylene diamine or diethylene triamine, in such a proportionas to leave at least one free amine group. Quaternized amido amines maysimilarly be employed. Alkyl phosphonium and hydroxyalkyl phosphoniumsalts having one C₈ to C₂₀ alkyl group and three C₁ to C₄ alkyl orhydroxyalkyl groups may also be used as cationic surfactants in thepresent invention. Typically the additional cationic surfactant may beany water soluble compound having a positively ionized group, usuallycomprising a nitrogen atom, and either one or two alkyl groups eachhaving an average of from C₈ to C₂₂. The anionic portion of the cationicsurfactant may be any anion which confers water solubility, such asformate, acetate, lactate, tartrate, citrate, chloride, nitrate, sulfateor an alkylsulfate ion having up to C₄ such as a higher alkyl sulfate ororganic sulfonate. Polyfluorinated anionic, nonionic or cationicsurfactants may also be useful in the compositions of the presentinvention. Examples of such surfactants are polyfluorinated alkylsulfates and polyfluorinated quaternary ammonium compounds.

Mixtures of two or more of the foregoing surfactants may be used. Inparticular mixtures of non-ionic surfactants with cationic and/oramphoteric and/or semi polar surfactants or with anionic surfactants maybe used. Typically mixtures of anionic and cationic surfactants areavoided, which are often less mutually compatible.

One preferred embodiment uses a surfactant including at least oneN-Alkyl-N-acylglucamine

wherein

-   Ra is a linear or branched, saturated or unsaturated    C₅-C₂₁-hydrocarbon residue, preferably a C₇-C₁₃-hydrocarbon residue,    and-   Rb is a C₁-C₄ alkyl residue, preferably methyl.

In another preferred embodiment, the N-Alkyl-N-acylglucamines compriseat least 50 wt.-% of the total amount of N-Alkyl-N-acylglucamines (8)compounds with C₇-C₉-alkyl residue and at least 50 wt.-% of the totalamount of N-Alkyl-N-acylglucamines (8) compound with C₁₁-C₁₃-alkylresidue.

In another embodiment, the surfactant is including at least one cyclicN-Aky-N-acylglucamine of the following formula

whereas in formula (9), (10) and (11)

-   Ra is a linear or branched, saturated or unsaturated C₅-C₂₁-alkyl    residue, preferably a C₇-C₁₃-alkyl residue, and-   Rb is a C₁-C₄-alkyl residue, preferably methyl.

The concentration of components A) and B) of the inventive embodimentsof the composition will provide a synergistic improvement of theperformance of component A) alone. The ratio between the components A)and B) may vary in the range of 5 wt % to 95 wt % and 95 wt % to 5 wt %.In a preferred embodiment, the concentration is in the range of 15 wt %to 85 wt % A) and 85 wt % to 15 wt % B). In another preferredembodiment, the weight ratio between A) and B) is A):B)=33 wt % to 66 wt%.

Whether or not there is a synergy between components A) and B) isdetermined by the reduced dose rate to prevent gas hydrate agglomerationover the dose rate required of each of the individual components.

In a second aspect, the instant invention provides a method forinhibiting gas hydrate formation, the method comprising bringing asystem containing hydrocarbons and water susceptible to gas hydrateformation in contact with the composition according to the first aspect.

In a third aspect, the instant invention provides the use of thecomposition according to the first aspect for inhibiting gas hydrateformation in a system containing hydrocarbons and water.

In a fourth aspect, the instant invention provides improved water dropproperties, including a reduction of the time to achieve significantwater drop and a reduction of the absolute amount of water remainingemulsified into the co-produced oil.

Preferably, R1 is an alkyl group having 3-4 carbon atoms and mostpreferred when R1 is an alkyl group having 4 carbon atoms;

Preferably, R2 is an alkyl group having 3-4 carbon atoms and mostpreferred when R1 is an alkyl group having 4 carbon atoms;

Preferably, R3 when present is hydrogen or organic moieties having from1 to 16 carbon atoms and most preferred when R3 is hydrogen;

Preferably, R4 is —(CH₂)_(t)— or —[CH₂—CHR₆)_(t)]— and most preferredwhen R4 is —(CH₂)_(t)—;

Preferably, R5 is an alkyl or alkenyl group having 8 to 22 carbon atomsand most preferred when R5 is an alkyl or alkenyl group having 8 to 18carbon atoms;

Preferably, R6 is hydrogen or an alkyl group having from 1 to 4 carbonatoms and most preferred when R6 is hydrogen;

Preferably, R7 is hydrogen or an alkyl group having from 1 to 4 carbonatoms and most preferred when R7 is hydrogen;

Preferably, R8 when present is hydrogen or an alkyl group having from 1to 4 carbon atoms and most preferred when R8 is hydrogen;

Preferably, n is 0 or 1 and most preferred when n=0

Preferably, m is 0 or 2 and most preferred when m=0

Preferably, o is 0 or 2 and most preferred when o=0

Preferably, p is 0 or 1 and most preferred when p=1

Preferably, t is 2, 3 or 4 and most preferred when t=3;

X⁻ is preferably selected from hydroxide, carboxylate, halide, sulfate,organic sulfonate, acrylate, methacrylate, and combinations thereof.Suitable halide ions include, without limitation, bromide, chloride, andcombinations thereof; X⁻ is more preferably selected from carboxylate,halide, acrylate, methacrylate, and combinations thereof; and is mostpreferred when X⁻ is acrylate.

In one preferred embodiment, R3 is hydrogen, and the anion X⁻ isselected from hydroxide, carboxylate, halide, sulfate, organicsulfonate, and combinations thereof.

In a still further embodiment, the compound according to formula (1) isthe reaction product of an N,N-dialkyl-aminoalkylamine with a fattyacid, a fatty acid ester or glyceride. Preferably, the fatty acid, esteror glyceride is derived from a plant source or an animal source,selected from coconut oil, tallow oil, vegetable oil, and combinationsthereof.

In another embodiment, the compound according to formula (1) includes aproduct prepared by the reaction of an amine selected from(3-dialkylamino)propylamine and (3-dialkylamino)ethylamine withvegetable oil or tallow oil followed by reacting with a reactantselected from an organic halide, such as an alkyl halide, having from 4to 20 carbon atoms, hydrogen peroxide, and an acid, wherein the acid isselected from mineral acids, formic acid, acetic acid, chloroaceticacid, propionic acid, acrylic acid, and methacrylic acid, and whereinthe dialkyl of the (3-dialkylamino)propylamine includes two alkyl groupsindependently selected from methyl, ethyl, propyl, butyl, morpholine,piperidine, and combinations thereof.

This invention relates to a method and a composition used therein forinhibiting, retarding, mitigating, reducing, controlling and/or delayingformation of hydrocarbon hydrates or agglomerates of hydrates. Themethod may be applied to prevent or reduce or mitigate plugging ofconduits, pipes, transfer lines, valves, and other places or equipmentwhere hydrocarbon hydrate solids may form under the conditions.

The term “inhibiting” is used herein in a broad and general sense tomean any improvement in preventing, controlling, delaying, reducing ormitigating the formation, growth and/or agglomeration of hydrocarbonhydrates, particularly light hydrocarbon gas hydrates in any manner,including, but not limited to kinetically, thermodynamically, bydissolution, by breaking up, other mechanisms, or any combinationsthereof.

The term “formation” or “forming” relating to hydrates is used herein ina broad and general manner to include, but are not limited to, anyformation of hydrate solids from water and hydrocarbon(s) or hydrocarbongas(es), growth of hydrocarbon hydrate solids, agglomeration ofhydrocarbon hydrates, accumulation of hydrocarbon hydrates on surfaces,any deterioration of hydrate solids plugging or other problems in asystem and combinations thereof.

The present method is useful for inhibiting hydrate formation for manyhydrocarbons and hydrocarbon mixtures. The method is particularly usefulfor lighter or low-boiling, C₁-C₅, hydrocarbon gases or gas mixtures atambient conditions. Non-limiting examples of such “low-boiling” gasesinclude methane, ethane, propane, n-butane, isobutane, isopentane andmixtures thereof. Other examples include various natural gas mixturesthat are present in many gas and/or oil formations and natural gasliquids (NGL). The hydrates of all of these low-boiling hydrocarbons arealso referred to as gas hydrates. The hydrocarbons may also compriseother compounds including, but not limited to CO₂, hydrogen sulfide, andother compounds commonly found in gas/oil formations or processingplants, either naturally occurring or used in recovering/processinghydrocarbons from the formation or both, and mixtures thereof.

The method of the present invention involves contacting a hydrocarbonand water mixture with a suitable compound or composition. When aneffective amount of the compound is used, hydrate blockage is preventedor at least delayed. In the absence of such effective amount, hydrateblockage is not prevented nor delayed.

The contacting may be achieved by a number of ways, including mixing,blending with mechanical mixing equipment or devices, stationary mixingsetup or equipment, magnetic mixing or other suitable methods, otherequipment and means known to one skilled in the art and combinationsthereof to provide adequate contact and/or dispersion of the compositionin the mixture. The contacting can be made in-line or offline or both.The various components of the composition may be mixed prior to orduring contact, or both. As discussed, if needed or desired, thecomposition or some of its components may be optionally removed orseparated mechanically, chemically, or by other methods known to oneskilled in the art, or by a combination of these methods after thehydrate formation conditions are no longer present.

Because the present invention is particularly suitable for lower boilinghydrocarbons or hydrocarbon gases at ambient conditions, the pressure ofthe condition is usually at or greater than atmospheric pressure. (i.e.about 101 kPa), preferably greater than about 1 MPa, and more preferablygreater than about 5 MPa. The pressure in certain formation orprocessing plants or units could be much higher, say greater than about20 MPa. There is no specific high-pressure limit. The present method canbe used at any pressure that allows formation of hydrocarbon gashydrates.

The temperature of the condition for contacting is usually below, thesame as, or not much higher than the ambient or room temperature. Lowertemperatures tend to favor hydrate formation, thus requiring thetreatment with the composition of the present invention. At much highertemperatures, however, hydrocarbon hydrates are less likely to form,thus obviating the need of carrying out any treatments.

The composition may also include solvent. These are generally solventsfor the virgin solid form of the compounds. Such solvents include, butare not limited to, water, simple alcohols like methanol, ethanol,iso-propanol, n-butanol, iso-butanol, 2-ethyl hexanol; glycols likeethylene glycol, 1,2-propylene glycols, 1,3-propylene glycol, andhexylene glycol; ether solvents like ethylene glycol mono butylether(butyl cellosolve), ethylene glycol dibutyl ether, and tetrahydrofuran;ketonic solvents like methylethylketone, diisobutylketone,N-methylpyrrolidone, cyclohexanone; armatic hydrocarbon solvents likexylene and toluene; and mixtures thereof. The selection of the suitablesolvent or combination of solvents are important to maintain a stablesolution of the compounds during storage and to provide stability andreduced viscosity for the inhibitor solutions when they are injectedagainst a pressure of 200 to 25,000 psi. The solvent preferably ispresent in the inhibitor composition in the range from 0% to about 95%,preferably from 20% to about 95%, more preferably from 50% to about 95%of the total composition, based on volume.

The compounds of the present invention are added into the mixture ofhydrocarbons and water at any concentration effective to inhibit theformation of hydrates under the given conditions. Preferably, theconcentration of the active gas hydrate inhibitor composition is betweenabout 0.01 wt.-% and about 5 wt.-% based on the water content. Morepreferably, the gas hydrate inhibitor composition concentration isbetween about 0.1 wt.-% and about 3 wt.-%.

The present invention may also be used in combination with other meansof hydrate inhibition such as the use of thermodynamic or kineticinhibitors discussed in the background section. These other hydrateinhibitors may be of the same or different type of hydrate inhibitorused in the composition. If mixtures of hydrate inhibitors are used, themixture may be added to the hydrocarbon and water containing processstream through a single port or multiple ports. Alternatively,individual hydrate inhibitors may be added at separate ports to theprocess stream.

The present invention may also be used in combination with other oilfield flow assurance and integrity compounds such as, but not limitedto, corrosion inhibitors, scale inhibitors, paraffin inhibitors,asphaltene inhibitors, drilling fluids, fracturing fluids, completionfluids, antifoams, emulsion breakers, and/water clarifiers.

EXAMPLES Test Procedure 1: Evaluation of Hydrate Inhibitor Compounds inParallel Process Development Reactors

To a 100 mL stainless steel reactor, attached to thermostat and a liquidhandling system, dodecane (10 mL), brine (20 mL of 5% NaCl, density of1.07 g/cm³ at 25° C.), and the anti-agglomerant formulation were addedat 30° C. The reactor was pressurized to 95 bar with Erdgas H (see Table1 for composition). The stirrer speed was adjusted to 1000 rpm for 1 minto saturate the liquid with gas. Subsequently the stirrer speed wasreduced to 200 rpm, and a temperature setting of −10° C. was initiated.Monitoring the internal temperature of the reactor showed acharacteristic exotherm indicative of hydrate formation below athreshold temperature. If the exotherm was accompanied by a prolongedincrease in stirrer power uptake this was indicative of agglomeration,signifying a failure. If the stirrer power remained constant orfollowing an increase returned to the original baseline, agglomerationwas prevented; indicating a pass.

For evaluation of their hydrate inhibitor performance, the testing wasstarted with 0.3 wt.-% of the hydrate inhibitor, formulated as a 60%active solution in methanol. If samples failed at this dose rate, theywere labelled as >0.3 wt.-% minimum effective dose (MED) and were nottested further. If samples initially tested at 0.3 wt.-% passed, theywere sequentially and incrementally reduced in dose rate by 0.05 wt.-%each time until a dose rate was used that failed. When that occurred,the last passing dose rate was input into the Table (4) as the MinimumEffective Dose (MED).

TABLE 1 Erdgas H gas composition Component Name Chemical Symbol Amount(mol-%) Nitrogen N₂ 0.14 Carbon Dioxide CO₂ 0 Methane C₁ 87.56 Ethane C₂7.6 Propane C₃ 3 i-Butane i-C₄ 0.5 n-Butane n-C₄ 0.8 i-Pentane i-C₅ 0.2n-Pentane n-C₅ 0.2

Monitoring of the internal temperature of the reactor shows acharacteristic exotherm indicative of hydrate formation below athreshold temperature. If the exotherm is accompanied by a prolongedincrease in stirrer power uptake this is indicative of agglomeration;signifying a failure. If the stirrer power remains constant or followingan increase returns to the original baseline, agglomeration isprevented; indicating a pass.

Water Drop Testing

When appraising Anti-Agglomerants, performance is obviously the highestcriteria to consider, however there are several secondary propertiesthat should also be considered that can have an effect on theoperational system to which the AA's are applied. It should be realizedthat both the primary criteria of performance as well as the secondaryproperties needs to be met for a particular chemistry or product to besuitable for use within an operational system. The water drop of theembodiments here (actives plus synergists), were surprisingly betterrelative to the standard AA's alone. When considering the water drop, atime period was chosen that would be considered aggressive (less time)for offshore separation, in part to ensure good translation to eventualfield application conditions. Specifically, at the total water drop(amount of expected water to be separated) was observed after vigorousmixing (created emulsion), with a time duration of 1 minute.

Experimental Details:

Into a graduated 100 mL cylinder with conical bottom (typically used foremulsion testing), 50 mL of oil and 50 mL of water were charged. Thewater was 6% brine (using NaCl) and the oil was a medium crude from theGulf of Mexico. To the 100 mL of total fluids 1 wt.-% in respect to theaqueous phase of a hydrate inhibitor (as a 60 wt.-% active formulation)were added. A dose rate of 1% was deliberately chosen to highlight theeffect of the hydrate inhibitors on the water drop. The bottles werecapped, shaken vigorously by hand, and allowed to stand at roomtemperature for 1 minute, at which point the amount of water that couldbe observed as a separate phase was recorded. This number was thenmultiplied by 2 to obtain the results shown in Table 4 as a percent ofwater present. A value of 100% means that all the water was observed asa separate phase. If less than 100% was observed, the remaining waterwas either within the oil or as part of a “rag layer” or emulsion layer.

For testing, gas hydrate inhibitor formulations were prepared byblending amphiphiles (A) according to table 2 and cationic surfactants(B) according to table 3 with the weight ratios according to table 4.For ease of handling, the formulations were adjusted to 60 wt.-% activecontent with methanol.

These formulations were tested for their minimum dosage rate for hydrateinhibition according to test procedure 1. The minimum dosage rates for apass given in table 4 refer to the required minimum dosage of activeingredient.

TABLE 2 Characterization of tested gas hydrate inhibitors A) accordingto Formula 1 wherein: Residue A1 A2 R¹ n-butyl n-butyl R² n-butyln-butyl R³ C₂H₅ H R⁴ —(CH₂)_(t)— —(CH₂)_(t)— R⁵ C₁₂H₂₅ Coco alkyl R⁶ H HR⁷ H — R⁸ — — m 0 0 n 1 0 o 2 0 p 1 1 t 3 3 u — — X⁻ ethyl sulfateacrylate

TABLE 3 Characterization of tested nonionic surfactants B) B1N-C₁₈-acyl-N-methyl-glucamide B2 C₈/C₁₀ Cyclic glucamide B3 (comp.)Sorbitan monolaurate B4 (comp.) Sorbitol C₈-C₁₈ fatty acid ester Cocoalkyl comprises as main components 51 wt.-% C₁₂H₂₅, and 16 wt.-% C₁₄H₂₉.

TABLE 4a Results from autoclave testing (components testing;comparative) Gas hydrate inhibitor (wt.-% active) MED water drop ExampleAmphiphile A Surfactant B (wt.-%) (%) 1 (comp.) A1 (100) — 0.30 80 2(comp.) A2 (100) — 0.30 84 3 (comp.) A3 (100) — 0.30 76 4 (comp.) A4(100) — 0.30 74 5 (comp.) — B1 (100) >0.30^((a)) 64 6 (comp.) — B2 (100)>0.30^((a)) 66 7 (comp.) — B3 (100) 0.30 60 8 (comp.) — B4 (100)>0.30^((a)) 62 ^((a))>0.30 wt.-% means it did not pass at 0.30 wt.-%dose rate and was not tested at higher concentration.

TABLE 4b Results from autoclave testing (formulations containing A1) Gashydrate inhibitor (wt.-% active) MED water drop Example Amphiphile ASurfactant B (wt.-%) (%) 9 A1 (50.0) B1 (50.0) 0.10 86 10 A1 (71.4) B1(28.6) 0.10 86 11 A1 (28.6) B1 (71.4) 0.15 86 12 A1 (50.0) B2 (50.0)0.10 88 13 A1 (71.4) B2 (28.6) 0.10 86 14 (comp.) A1 (50.0) B3 (50.0)0.25 82 15 (comp.) A1 (71.4) B3 (28.6) 0.30 82 16 (comp.) A1 (50.0) B4(50.0) 0.25 80 17 (comp.) A1 (71.4) B4 (28.6) 0.20 80

TABLE 4c Results from autoclave testing (formulations containing A2) Gashydrate inhibitor (wt.-% active) MED water drop Example Amphiphile ASurfactant B (wt.-%) (%) 18 A2 (50.0) B1 (50.0) 0.10 94 19 A2 (71.4) B1(28.6) 0.10 96 20 A2 (50.0) B2 (50.0) 0.10 96 21 A2 (71.4) B2 (28.6)0.05 94 22 A2 (28.6) B2 (71.4) 0.15 94 23 (comp.) A2 (50.0) B3 (50.0)0.30 90 24 (comp.) A2 (71.4) B3 (28.6) 0.25 88 25 (comp)  A2 (50.0) B4(50.0) 0.25 88 26 (comp.) A2 (71.4) B4 (28.6) 0.20 88

1. A method for inhibiting gas hydrate formation in a system containinghydrocarbons and water, comprising the step of contacting the systemwith a composition comprising A) from 5 to 95 weight-% of a compoundaccording to formula (1)

wherein R1 is an alkyl group having from 1 to 5 carbon atoms; R2 ishydrogen or an alkyl group having from 1 to 5 carbon atoms; R3 ispresent or not as hydrogen and organic moieties having from 1 to 20carbon atoms; R4 is selected from —(CH2)t-, —[(CH2-CHR6)t]-,—(CH2-CHR6O)u-(CH2)t- and combinations thereof; R5 is an alkyl oralkenyl group having 4 to 22 carbon atoms; R6 is hydrogen or an alkylgroup having from 1 to 4 carbon atoms; R7 is hydrogen or an alkyl grouphaving from 1 to 4 carbon atoms; R8 is present or not as hydrogen ororganic moieties having from 1 to 20 carbon atoms; t is 2, 3 or 4; u isan integer between 0 and 100; n is 0 or 1 m is 0 or 2 o is 0 or 2 p is 0or 1 X− is an anion, and B) from 5 to 95 weight-% of a synergisticsurfactant which is selected from the group consisting of N-acylatedpolyhydroxyalkylamines.
 2. The method for inhibiting gas hydrateformation in a system containing hydrocarbons and water according toclaim 1, wherein B) is from 5 to 95 weight-% of a synergistic surfactantwhich is selected from the group consisting of N-acylatedpolyhydroxyalkylamines according to formula (19)

wherein Z is the polyhydroxyalkyl radical of a monosaccharide oroligosaccharide; R¹¹ is an alkyl or alkenyl group having 8 to 18 carbonatoms; and R¹² is an alkyl group having from 1 to 5 carbon atoms.
 3. Themethod for inhibiting gas hydrate formation in a system containinghydrocarbons and water according to claim 1, wherein X− is selected fromthe group consisting of hydroxide, carboxylate, halide, sulphate,organic sulphonate, acrylate, methacrylate, and combinations thereof. 4.The method for inhibiting gas hydrate formation in a system containinghydrocarbons and water according to claim 1, wherein the synergisticsurfactant includes at least one N-Alkyl-N-acylglucamine

wherein Ra is a linear or branched, saturated or unsaturatedC₅-C₂₁-hydrocarbon residue, and Rb is a C₁-C₄ alkyl residue.
 5. Themethod for inhibiting gas hydrate formation in a system containinghydrocarbons and water according to claim 1, wherein R3 is hydrogen, andthe anion X⁻ is selected from the group consisting of hydroxide,carboxylate, halide, sulphate, organic sulphonate, and combinationsthereof.
 6. The method for inhibiting gas hydrate formation in a systemcontaining hydrocarbons and water according to claim 1, wherein the stepof contacting may be achieved by mixing, blending with mechanical mixingequipment or devices, stationary mixing setup or equipment, magneticmixing or other suitable methods, other equipment known to one skilledin the art or combinations thereof to provide adequate contact and/ordispersion of the composition in the mixture.
 7. The method forinhibiting gas hydrate formation in a system containing hydrocarbons andwater according to claim 1, wherein the step of contacting can be madein-line or offline or both.
 8. The method for inhibiting gas hydrateformation in a system containing hydrocarbons and water according toclaim 1, wherein the pressure is at or greater than atmosphericpressure.
 9. The method for inhibiting gas hydrate formation in a systemcontaining hydrocarbons and water according to claim 1, wherein thepressure is greater than about 1 MPa.
 10. The method for inhibiting gashydrate formation in a system containing hydrocarbons and wateraccording to claim 1, wherein the composition further comprises at leastone solvent.
 11. The method for inhibiting gas hydrate formation in asystem containing hydrocarbons and water according to claim 10, whereinthe solvent is selected from the group consisting of water, methanol,ethanol, iso-propanol, n-butanol, iso-butanol, 2-ethyl hexanol, ethyleneglycol, 1,2-propylene glycols, 1,3-propylene glycol, hexylene glycol,ethylene glycol mono butylether (butyl cellosolve), ethylene glycoldibutyl ether, tetrahydrofuran, methylethylketone, diisobutylketone,N-methylpyrrolidone, cyclohexanone, xylene, toluene, and mixturesthereof.
 12. The method for inhibiting gas hydrate formation in a systemcontaining hydrocarbons and water according to claim 10, wherein thesolvent is present in the inhibitor composition in the range from 0.1%to about 95%, based on the volume of the inhibitor composition.
 13. Themethod for inhibiting gas hydrate formation in a system containinghydrocarbons and water according to claim 1, wherein the concentrationof the compound according to formula (1) is between about 0.01 wt.-% andabout 5 wt.-% based on the water content.
 14. The method for inhibitinggas hydrate formation in a system containing hydrocarbons and wateraccording to claim 1, wherein the composition further comprisesthermodynamic or kinetic gas hydrate inhibitors.
 15. The method forinhibiting gas hydrate formation in a system containing hydrocarbons andwater according to claim 1, wherein R¹ is n-butyl, R² is n-butyl, R³ isC₂H₅, R⁴ is —(CH₂)_(t)—, R⁵ is C₁₂H₂₅, R⁶ is H, R⁷ is H, R⁸ is notpresent, m is 0, n is 1, o is 2, p is 1, t is 3, u is not present, andX⁻ is ethyl sulfate.
 16. The method for inhibiting gas hydrate formationin a system containing hydrocarbons and water according to claim 1,wherein R¹ is n-butyl, R² is n-butyl, R³ is H, R⁴ is —(CH₂)_(t)—, R⁵ iscoco alkyl, R⁶ is H, R⁷ is not present, R⁸ is not present, m is 0, n is0, o is 0, p is 1, t is 3, u is not present, and X⁻ is acrylate.
 17. Acomposition for inhibiting gas hydrate formation in a system containinghydrocarbons and water, comprising A) from 5 to 95 weight-% of acompound according to formula (1)

wherein R1 is an alkyl group having from 1 to 5 carbon atoms; R2 ishydrogen or an alkyl group having from 1 to 5 carbon atoms; R3 ispresent or not as hydrogen and organic moieties having from 1 to 20carbon atoms; R4 is selected from —(CH2)t-, —[(CH2-CHR6)t]-,—(CH2-CHR6O)u-(CH2)t- and combinations thereof; R5 is an alkyl oralkenyl group having 4 to 22 carbon atoms; R6 is hydrogen or an alkylgroup having from 1 to 4 carbon atoms; R7 is hydrogen or an alkyl grouphaving from 1 to 4 carbon atoms; R8 is present or not as hydrogen ororganic moieties having from 1 to 20 carbon atoms; t is 2, 3 or 4; u isan integer between 0 and 100; n is 0 or 1 m is 0 or 2 o is 0 or 2 p is 0or 1 X− is an anion, and B) from 5 to 95 weight-% of a synergisticsurfactant which is selected from the group consisting of N-acylatedpolyhydroxyalkylamines.
 18. The composition according to claim 17,wherein R¹ is n-butyl, R² is n-butyl, R³ is C₂H₅, R⁴ is —(CH₂)_(t)—, R⁵is C₁₂H₂₅, R⁶ is H, R⁷ is H, R⁸ is not present, m is 0, n is 1, o is 2,p is 1, t is 3, u is not present, and X⁻ is ethyl sulfate.
 19. Thecomposition according to claim 17, wherein R¹ is n-butyl, R² is n-butyl,R³ is H, R⁴ is —(CH2)t-, R⁵ is coco alkyl, R⁶ is H, R⁷ is not present,R⁸ is not present, m is 0, n is 0, o is 0, p is 1, t is 3, u is notpresent, and X− is acrylate.
 20. A method for inhibiting gas hydrateformation in a system containing hydrocarbons and water, comprising thestep of contacting the system with a composition comprising A) from 5 to95 weight-% of a compound according to formula (1a)

wherein R1 is an alkyl group having from 1 to 5 carbon atoms; R2 ishydrogen or an alkyl group having from 1 to 5 carbon atoms; R3 ispresent or not as hydrogen and organic moieties having from 1 to 20carbon atoms; R4 is selected from —(CH₂)_(t)—, —[CH₂—CHR⁶)_(t)]—,—(CH₂—CHR⁶O)_(u)—(CH₂)_(t)— and combinations thereof; R5 is an alkyl oralkenyl group having 4 to 22 carbon atoms; R6 is hydrogen or an alkylgroup having from 1 to 4 carbon atoms; R7 is hydrogen or an alkyl grouphaving from 1 to 4 carbon atoms; R8 is present or not as hydrogen ororganic moieties having from 1 to 20 carbon atoms; t is 2, 3 or 4; u isan integer between 0 and 100; n is 0 or 1 m is 0 or 2 o is 0 or 2, p is0 or 1, q is an integer between 0 and 2 X⁻ is an anion, wherein q is 0when R3 and R8 are absent; q is 1 when one of R3 and R8 is present andthe other is absent; and q is 2 when R3 and R8 are both present and B)from 5 to 95 weight-% of a synergistic surfactant which is selected fromthe group consisting of N-acylated polyhydroxyalkylamines.
 21. Acomposition for inhibiting gas hydrate formation in a system containinghydrocarbons and water, comprising A) from 5 to 95 weight-% of acompound according to formula (1a)

wherein R1 is an alkyl group having from 1 to 5 carbon atoms; R2 ishydrogen or an alkyl group having from 1 to 5 carbon atoms; R3 ispresent or not as hydrogen and organic moieties having from 1 to 20carbon atoms; R4 is selected from —(CH₂)_(t)—, —[CH₂—CHR⁶)_(t)]—,—(CH₂—CHR⁶O)_(u)—(CH₂)_(t)— and combinations thereof; R5 is an alkyl oralkenyl group having 4 to 22 carbon atoms; R6 is hydrogen or an alkylgroup having from 1 to 4 carbon atoms; R7 is hydrogen or an alkyl grouphaving from 1 to 4 carbon atoms; R8 is present or not as hydrogen ororganic moieties having from 1 to 20 carbon atoms; t is 2, 3 or 4; u isan integer between 0 and 100; n is 0 or 1 m is 0 or 2 o is 0 or 2, p is0 or 1, q is an integer between 0 and 2 X⁻ is an anion, wherein q is 0when R3 and R8 are absent; q is 1 when one of R3 and R8 is present andthe other is absent; and q is 2 when R3 and R8 are both present and B)from 5 to 95 weight-% of a synergistic surfactant which is selected fromthe group consisting of N-acylated polyhydroxyalkylamines.